Security Officers pulling misidentified items for inspection has been an issue since X-ray machines were incorporated into the security environment. Every time this occurs at an airport, the airport needs to report it as an X-ray Access Control Event. The use of a Manual Diverter Roller (MDR) and Alternate Viewing Station (AVS) in the checkpoint scanning process increases the instances of wrong bag pulls. The X-ray Security Officer viewing the X-ray display can select an item for additional screening. However, due to the nature of some X-ray systems, the x-ray Security officer may need to advance the belt forward to enable the item in question to exit the machine and be pulled from the system's tube to the MDR. The item sits on the MDR, sometimes behind other items, awaiting inspection. When the Property Search Officer (PSO) takes the suspect item from the MDR to the AVS and pulls up the X-ray image, the PSO may then realize that the contents of the bag and the X-ray image do not match. This may be due to the X-ray Security Officer having selected the wrong (i.e., mismatched) bag for secondary search. It can be difficult to locate the actual item that the X-ray officer wanted to select for additional screening, and the passenger may not still be located in the security checkpoint screening area and may have boarded a plane. Furthermore, the item may be so dangerous that an airport will have to force everyone out of the sterile area, sweep the airport, and rescreen all passengers. This can create logistical nightmares for airport operations with the potential to become catastrophic events, due to such X-ray access control violations. A wrong bag pull represents a temporary loss of security containment that can be minor or escalate into a highly publicized media event or worse, a true risk to the transportation security network.
Airports and vendors have tried other methods to prevent this type of access control event: confer and concur where two officers make a decision on whether the correct bag/item is being pulled, using reflective numbers on bins, arranging orientations of like items in different configurations, and so on. These solutions do not work because they do not address the root cause or they require TSO assistance or the passenger to divest differently. In some instances, markers used on belts create confusion in single-scanner X-ray systems (markers appearing backward when the upper and lower belt sections are imaged together in a bottom-up scanner), and would be completely unworkable in multiple-scanner situation (where double or repeat markers would appear in the composite images, resulting in inability to tell which marker happened to be located on a top surface of the belt).